The present invention relates to heart valve prostheses generally and more particularly relates to mechanical bileaflet prosthetic heart valves.
Heart valve prostheses are well known in the art. Generally speaking, heart valve prostheses can be classified in two major types or categories. One type of prosthesis employs a tissue valve of animal (usually porcine) origin in its blood flow regulating valve mechanism. The other type of heart valve prosthesis utilizes a ball, a disc, valve leaflets or other mechanical devices to regulate the direction of blood flow through the prosthesis. The latter type of prosthesis is usually known in the art as "mechanical" heart valve prosthesis. For specific examples and detailed descriptions of the heart valve prostheses of the prior art, reference is made to U.S. Pat. Nos. 3,744,062; 3,835,475; 3,997,923; 4,364,126 and 4,106,129.
By their very nature, the mechanical heart valve prostheses have metal or plastic surfaces which, when exposed to the blood flow, are thrombogenic to some degree related to deficiencies in design, physical structure, operational characteristics and structural material. In more recent years, pyrolytic carbon coated bileaflet heart valves having flat leaflets of the type shown in U.S. Pat. Nos. 4,276,658; Re. 31,040; 4,935,030; 4,863,458; 4,822,353; 4,888,010; 4,272,854; 4,451,937; 4,689,046; and 4,863,467, as well as PCT Publication No. W089/00841, have been published. Other prosthetic heart valves of the type shown in U.S. Pat. Nos. 4,484,365, 4,950,287 and 4,863,459, disclose leaflets curved in the downstream direction. A further group of designs employing conical or cylindrical surface leaflets and pivot axes adjacent to or somewhat displaced from the center of the valve wherein the leaflets typically open away from the center of the valve to provide for central blood flow are disclosed in U.S. Pat. Nos. 4,808,180; 4,363,142; 4,274,437; 4,446,577; 4,328,592; 4,308,624; 4,443,894; 4,357,715; 4,308,624; 4,488,318; and 4,676,789.
Such heart valve designs having a variety of shapes of the leaflets and configurations of hinges have been developed in an effort to improve reliability, hemodynamics, ease of surgical implantation, and the reduction or elimination of the development of thrombi.
However, some of the prior art heart valve prostheses have designs which are functionally inefficient and resistive to the free passage of blood. Others cause blood stagnation points or regions and turbulence which results in the formation of blood clots on the valve structure to obstruct the normal leaflet movement. Hemolysis (destruction of blood elements) is still a concern in prior art valves that have fast closing contact speed and momentum by which blood elements are mechanically crushed.
In prior designs, considerable attention has been paid to the hinge mechanisms and particular shapes of the bileaflet valves in an effort to improve the blood flow characteristics through the valve orifice in its open position, to reduce the pressure drop and turbulence caused by the profiles of the leaflets to flowing blood. Designs intended to reduce noise of closure of the leaflets, and to provide for continuous cleaning of the valve surfaces and wiping of the hinges have also been advanced in the listed patents. The above listed patents depict various hinge mechanisms that provide rotation and in certain instances, translation of the leaflets during the opening and closing phases. However, most of these designs have never been utilized due to a variety of design shortcomings listed above.
In this regard, to avoid clotting of blood, it is desirable to make further improvements in mechanical heart valve prostheses with regard to these characteristics as well as with regard to simplicity and cost of construction, reliability of operation, and reduction of thrombogenecity. The mechanical heart valve of the present invention provides such improvements.